Polyketones having a structure in which repeating units derived from carbon monoxide and repeating units derived from ethylenically unsaturated compounds are substantially alternately connected with each other are excellent in mechanical properties and thermal properties and high in wear resistance, chemical resistance and gas barrier properties, and thus are expected to be used in various fields. For example, polyketones are useful material as resins, fibers and films having high strength and high heat resistance. Particularly, when a high molecular weight polyketone having an intrinsic viscosity of 2.5 dl/gd or higher is used as a raw material, fibers or films having very high strength and elastic modulus can be obtained. These fibers or films are expected to be used in the wide variety of applications of constructional materials and industrial materials, e.g., belts, hoses, rubber reinforcing materials such as tire cords, concrete reinforcing materials, etc.
Polyketones mainly composed of repeating units comprising ethylene and carbon monoxide have a high melting point of 200° C. or higher, nevertheless, they suffer from the problems that thermal modifications such as three-dimensional crosslinking occur under heating for a long period of time to cause deterioration of molding processability due to loss of flowability, and furthermore mechanical performance and heat resistance performance of the molded products are lowered owing to decrease of the melting point.
As a method for molding a polyketone into fibers or films with high strength, a wet molding method which comprises molding a polyketone dissolved in an aqueous solution of an inorganic salt, such as zinc chloride (e.g. WO99/18143 pamphlet and WO00/09611 pamphlet). However, in this method, there are problems that long-term heating of a dope in which polyketone is dissolved causes thermal modification of the polyketone which results in the deterioration of flowability and spinnability of the dope and that mechanical properties of the resulting fibers or films are thus deteriorated.
If a polyketone is heated, it undergoes chemical reactions, such as Paal-Knorr reaction to produce a furan ring and the formation of intramolecular or intermolecular crosslinking due to aldol condensation, resulting in the progress of heat deterioration of the polyketones. These chemical reactions are considerably accelerated by the polymerization catalyst (palladium (Pd)) remaining in polyketones. As measures against the heat deterioration, techniques of reducing the amount of Pd remaining in polyketones have been proposed (e.g., European Patent No. 285218, U.S. Pat. No. 4,855,400 and U.S. Pat. No. 4,855,401). The reduction of the amount of Pd remaining in polyketones brings about an effect of improving the heat resistance of polyketones. However, the techniques disclosed in the above publications are methods comprising: subjecting a polyketone obtained by a conventional polymerization method to a lengthy Pd extraction treatment using a compound, such as triphenylphosphine, triethylamine or 1,3-bis{di(2-methoxyphenyl)phosphino}propane. Therefore, these methods cannot be put to industrially practical use, taking into consideration the costs for washing facilities, and washing and extracting solvents. Furthermore, since heat deterioration of polyketones also occurs due to the lengthy heat treatment, the heat resistance of the resulting polyketones is not sufficient, although the Pd content is small.
“Polymer”, 42 (2001) 6283-6287 discloses that a polyketone obtained by polymerization in acetone solvent is subjected to the extraction treatment with 2,4-pentanedione to reduce the Pd content to 20 ppm or less, whereby the heat resistance of the polyketone can be improved. Regarding this polyketone, the polymerization activity obtained under the above conditions is very low because no alcohol is used as a polymerization solvent. Moreover, since the complicated Pd extraction treatment must be carried out after the polymerization, the method cannot be industrially employed from the viewpoints of productivity and cost.
WO00/09611 pamphlet shows a polyketone having a Pd content of 5 ppm. However, this polyketone is obtained by effecting the polymerization at 80° C. under 5 MPa and then removing Pd in the polymer by solvent extraction. The method thus has problems that the polymerization rate is very low and that lengthy heat treatment is required during the solvent extraction.
In order to reduce the Pd content in polyketone without carrying out the lengthy extraction treatment, it is necessary to produce a large amount of polyketone with a small amount of Pd, namely, to carry out a polymerization for a long time with high polymerization activity. Some techniques are known as polymerization method with high polymerization activity. For example, JP-A-1-201333, JP-A-2-115223, and WO00/68296 pamphlet and WO01/02463 pamphlet disclose polymerization techniques with the very high polymerization activity which exceeds 20 kg/g-Pd/hr. Here, the polymerization activity is an index (unit: kg/g-Pd/hr) which shows an amount of polymer produced per unit of time with the use of a unit amount of a catalyst (Pd in the present invention). The greater its value is, the larger the amount of polyketone obtained from a unit amount of Pd is.
However, all the polyketones obtained by the polymerization methods with high polymerization activity (20 kg/g-Pd·hr or higher) disclosed in the above publications have low polymerization degree and the intrinsic viscosity lower than 2.5 dl/g. The techniques are thus insufficient to be used for fibers or films with high strength.
With reference to the terminal structure of polyketones, studies have been carried out on the relation between the kind of polymerization solvent and the structure and ratio of the terminals produced. It is known that the terminal structure of polyketones varies depending on the kind of solvents used for the polymerization. Chem. Rev., 96 (1996), 663-681 proposes the following mechanisms (reaction formula I to reaction formula VI) in the polymerization reaction of polyketone in methanol, which show that an alkyl ester terminal (reaction formulas I, V) and an alkyl ketone terminal (reaction formulas II, VI) are produced in the initiation reactions and termination reactions. In the following reaction formulae, L2 denotes a phosphorus bidentate ligand and Pol denotes a molecular chain of polyketone polymer.
(Initiation Reaction)
Reaction Formula II:
(Growth Reaction)

(Termination Reaction)


Furthermore, JP-A-59-197427 discloses the terminal structures and ratio thereof in the case of using various polymerization solvents with 1,3-bis(diphenylphosphino)propane as a phosphorus ligand. For example, it is disclosed that when an alcohol, such as methanol or ethanol, is used, an alkyl ester terminal and an alkyl ketone terminal are produced, when a glycol, such as ethylene glycol, is used, a hydroxyalkyl terminal and an alkyl ketone terminal are produced, and when a non-protonic polar solvent, such as tetrahydrofuran or acetone, is used, only an alkyl ketone terminal is produced. The above publication discloses that when an alkyl ester terminal is produced, the equivalent ratio of alkyl ester terminal (terminal group A)/alkyl ketone terminal (terminal group B) is not 1/1, but 0.09/1-1.04/1. However, polyketones illustrated in the above publication are all polymers with low molecular weights and the publication makes no mention of polyketones with high molecular weights having an intrinsic viscosity of 2.5 dl/g or higher. Specifically, the polyketones having terminal group A and terminal group B that are shown in Examples of the publication have a number-average molecular weight of 250-7500. When the intrinsic viscosity is calculated using the formula (Intrinsic viscosity=1.0×10−4×Mw0.85) described in a publication (e.g., JP-A-4-228613) with proviso that the molecular weight distribution (Mw/Mn) is 3.3 which is a value of general polymers, the intrinsic viscosity of the polyketones described in the Examples is 0.03-0.54 dl/g, and hence the polyketones cannot be expected to exhibit high mechanical characteristics of high strength and high elastic modulus.
Moreover, regarding the polyketones disclosed in the publication, the polymerization activity is very low, and the theoretical Pd content in the polyketones, which is calculated from the product of polymerization activity and polymerization time (catalyst efficiency) is 100 ppm or more. Thus, the polyketones contain a considerably large amount of Pd.
Regarding the terminal groups of polyketones, studies are conducted on the polymerization conditions and the structure and ratio of the produced terminals, nevertheless, regarding the relation between the terminal structure and the characteristics of polyketones, it is merely disclosed, for example, in JP-A-2-16155 that the characteristics of polyketones do not depend on the structure of the terminal groups. Particularly, no disclosure is made as to the control of structure of terminal group as a means to improve the heat stability of polyketones in an aqueous solution of a metal salt.
The object to be solved in the present invention is to provide a polyketone that has a high molecular weight, exhibits high mechanical characteristics and excellent heat resistance and chemical resistance when molded into the products, such as fibers and films, and can be used as inexpensive industrial starting materials. Such a polyketone has not been obtained by known techniques. The further object to be solved in the present invention is to provide a method for producing the polyketone in a highly productive manner with high polymerization activity without carrying out complicated steps, such as catalyst extraction treatment.